Anisotropic superhydrophobic surfaces

In the case of a charged gas interface (only) a considerable enhancement of electro-osmotic flow is possible. For a uniformly charged (qi = q2 = qo) anisotropic superhydrophobic surface, the expression for electro-osmotic flow can be transformed to ... 

W. Li, G.P. Fang, Y.F. Lij, G.J. Qiao, Anisotropic wetting behavior arising from superhydrophobic surfaces parallel grooved structure. J. Phys. Chem. B 112(24), 7234-7243 (2008)... 

Surfaces that possess directionally dependent or anisotropic superhydropho-bicity have been the subject of a number of studies due to their potential application in microfluidic devices, their ability to form evaporation-driven surface patterns, and their potential to form coatings that are readily cleaned (Higgins and Jones, 2000 Liu et al., 2006, 2010). Anisotropic superhydro-phobicity has been observed on the surfaces of a number of plants and insects, including rice leaves and butterfly wings (Figure 5). These surfaces were found to exhibit properties associated with anisotropic hydropho-bicity, these being low water drag, superhydrophobicity, and the abihty to self-clean (Bixler and Bhushan, 2012, 2013), properties that arise from the unique hierarchical structures present on the surface (Bixler and Bhushan, 2013). 

Figure 5 The anisotropic surface structures of (A) rice leaves and (B) butterfly wings. The superhydrophobic structures present on both surfaces are directionally ordered, resulting in a variable wettability that is dependent on the direction of movement. Guo and Liu (2007), Peng etal.(2011).

---